Exposing rd_kafka_conf_dump? How?

[aesteve]

Hello, not sure that's the right place to ask, but it's not really an issue, and not (yet?? hopefully) a PR.

rdkafka_sys has a method called rd_kafka_conf_dump that's handy to log the client configuration for investigations.

I haven't found it in rust-rdkafka so I came up with this implementation:

use std::collections::HashMap;
use std::ffi::CStr;
use std::str::Utf8Error;
use rdkafka::ClientConfig;
use rdkafka::error::KafkaError;


#[derive(Debug)]
pub(crate) enum ConfDumpError {
    NativeConfError(KafkaError),
    ByteStrError(Utf8Error)
}

impl From<KafkaError> for ConfDumpError {
    fn from(err: KafkaError) -> Self {
        NativeConfError(err)
    }
}

impl From<Utf8Error> for ConfDumpError {
    fn from(err: Utf8Error) -> Self {
        ByteStrError(err)
    }
}

pub(crate) unsafe fn conf_dump(config: &ClientConfig) -> Result<HashMap<String, String>, ConfDumpError> {
    let native_config = config.create_native_config()?;
    let mut size = 0;
    let ptr = rdkafka_sys::rd_kafka_conf_dump(native_config.ptr(), &mut size);
    let mut map = HashMap::with_capacity(size / 2);
    let mut i = 0;
    while i < size - 1 {
        let k_raw = *ptr.add(i);
        i += 1;
        let v_raw = *ptr.add(i);
        let k = CStr::from_ptr(k_raw).to_str()?;
        let v = CStr::from_ptr(v_raw).to_str()?;
        map.insert(k.to_string(), v.to_string());
        i += 1;
    }
    Ok(map)
}

I'm not a lot experienced in Rust, so that's still probably not a good candidate for a PR, but:

1. Do you think the feature is needed? (to be included in rust-rdkafka?)
2. If yes, do you see any improvement to the code above to make it better? So that I can submit a PR?
   (note: especially, maybe there's an already existing way to deal with pointers over a string iterator that doesn't involve all the ptr.add(i)? I draw inspiration from CreateTopicResult iirc, but since that's the very 1st time I'm writing FFI-related code, huge chances are missed the point entirely)

Thanks!